Method for producing highly-refractory magnesite masses



' Patented Feb. 14, 1928.

UNITED-(STATES PATENT OFFICE.

FELIX BAUMHAUEB, OF MANNHEIM-WALDHOF, GERMANY, ASSIGNbR TO THE FIB H:

IUYNAMIDON-WERK ENGELHORN 00., GESELLSCHAFT MIT BES CHRANKTEB, HAI- TUNG, OF MANNHEIM-WALDHOF, GERMANY.

METHOD FOR PRODUCING HIGHLY-REFRACTORY MAGNESIT E HASSES.

Ho Drawing. Application filed February 16, 1924, Serial No. 693,387,-and in Germany February 20, 1923.

The invention relates to the producing highly refractory magnesite masses and to such masses and utensils, that possess an exceptional degree of constancy in volume,

stability and resistance to changes in temperature. The invention makes possible the production'of such products out of different starting-materials.

It has been found that highly refractory magnesite masses, constant in volume, stable under high temperatures and insensible toq 'tically burnt and, after having been cooled,

is ground to such a degree of 1m alpability that there remains an inapprecia le residue on the sieve of 5000 meshes per sq. cm. An exaggerated owdering may turn out to be unfavorab e under given circumstances. The powder obtained in this manner is briquetted and com actly sintered at about 1500 to 1600 C. n this manner the compressed bodies acquire a completely tight and compact ed magnesite. A y

In place of grinding magnesia in dry state it can also be prepared according to the wetprocess. In such case'it is advisable to caustically burn magnesite, poor in fluxing agents, in such a way that after the buming process it exhibits a maximum of waterabsorbing power. The so burnt magnesite is then ground as above to the fineness of a sieve of 5000 meshes per sq. .cm., and this with a small quantity of water in excess of that which is required for the hardening operation. When the paste is heated for a short period, the mass becomes stifi, with development of heat. Therenpon the hydrate of magnesium formed is briquetted and compactly sintered at 1500 to1600 C.

; The material obtained by the foregoipig' ways is in the known manner grain, greatly resembling meltgranulated, ground and sifted, and with the addition of cribblcd fine powder that has traversed a sieve with 5000 meshes per sq. cm. as a binding agent is shaped or compressed and reduced to bricks. In its natural state the sintered and crushed mass can agent. An addition of a few percent of cla or other binding-agents facilitates accor i ng to the circumstances the shaping without essentially reducing the fire-proof quality.

In shaping also combustible binding agents,

such as starch, tar or its equivalents can be made available under given circumstances.

It has been furthermore found that magnesite masses of unrivalled stability and in sensibility to changes in temperature can be produced from raw magnesltes, containing no or only a limited percentage of flux-accelerating agents, in the event that these magnesites are not sintered but melted. To ensure suchetfect any magnesite containing only a slight amount of lime can be made available. Even ferriferous magnesites can be employed as a starting material if during the melting process care has been taken to reduce and separate out the ferric combinations. Atall events magnesites poor in iron are best suitable and also to be preferred from "an economical point ofview.

According to the present process magnesites, preferablv those containing a possible minimum of lime and iron. are melted in a convenient way. this being done in the electric areor resistance furnace. The melted mass is crushed and the coarse-grained material is used. with the addition asa binding agent, of melted magnes te, ground to the high degree of impalpability. Besides melted fine material sintered or caustically burnt magnesite or magnesia enter into account. The masses obtainedcan serve either immediately--without being brought into shape-in form of mortar, mastic, coating, fettling material or, by means of compression. they are shaped into bricks and keenly burnt. i

Both rawand previously sintered or else caustically burnt magnesite can serve as a starting material for the melting process.

Also artificially produced magnesia can be used provided that it is suiliciently free from flux-accelerating agents.

hen using ferriferous magnesites the process should be conducted in such a way that inthe melting operation the iron is reduced as much as possible for subsequent operation thus allowing its removal from the melted mass after comminut'ion by means of magnets.

It is a surprising fact that the melted magnesite can be bound by nonplastic fine material of the same kind. The best proportion in which to add this finely ground melted material to the granulated material is an addition of from 10 to 20%. i

As before mentioned a portion of this melted binding agent can also be replaced by sintered or caustically burnt magnesite material or by magnesia. \Vith a view to give a greater resisting power to the compressed or moulded composition prior to submitting it to the burning process, an easily apglicable binding agent such as tar, dextrin or its equivalents can be added.

The dressing of the masses and the burning of the raw-formed bricks are done in the manner used in the industry of refractory materials. They should be burnt as keenly as p0ssible.

Compositions produced and articles burnt in this way possess a fire-proof quality exceeding by far 2000 C. They are constant in volume and yet absolutely stable when exposed to strong pressure at highest temperatures. This makes it ossible to construct highly strained walls with magnesite-bricks,

produced according to the present method, evenfor excessively heated kilns, without having to risk signs of softening or crumbling.

The melted magnesite masses stand strong changes in temperature without cracking. Even quick heating up or sudden cooling down has no eti'eet on it.

Further the masses possess increased resistance to chemical attacks and scorifying substances.

Claims:

1. The method of making a refractory, which comprises melting magnesite containing an iron compound as an impurity, and reducing the iron, grinding the product, separating substantially all of the iron, granulating the product and binding the same with finely ground product. 7

2. The method of making arefractory, which comprisesmelting magnesite, granulating the product and adding to the product finely ground sintered magnesite sufiicient to bind the same.

3. The method of making a refractory,

which comprises calcining magnesite su stantially free of fluxing material, pulverizing, and pressing the calcined magnesite into shapes, sintering it at temperatures slightly below 17 00 0., granulating the product and adding to the granulated sintered product finely ground sintered product sufiicient to bind the same.

In testimony that I claim the foregoing as my invention, I have signed my name.

FELIX BAUMHAUER. 

